Residual Flexural Performance and Performance-Normalized Embodied Carbon of Recycled and Commercial Steel Fibers in Slag-Blended Concrete

This study introduces a decision-oriented framework integrating fresh-state rheology, standardized post-cracking performance, and cradle-to-gate embodied carbon for steel-fiber-reinforced concretes incorporating recycled and commercial fibers. The motivation lies in achieving mechanical efficiency while reducing the environmental burden of cementitious composites. Mixtures were produced with water-to-binder ratios between 0.40 and 0.60, fiber dosages of 15–45 kg/m³, and 50% GGBS replacement to mitigate binder-related carbon emissions. Equal-workability comparisons were conducted at 15 kg/m³ using ICAR-based static yield stress measurements, whereas higher dosages were evaluated without rheology-based adjustment. Post-cracking performance was assessed through residual flexural strengths at CMOD = 0.5 and 2.5 mm (f_R1, f_R3) and CMOD-based toughness indices. Embodied performance was quantified using the embodied-carbon-per-performance (ECP) index, normalized by f_R3. Results indicate that recycled fibers exhibit greater fresh-state resistance but slightly lower residual capacities under equal workability, while commercial fibers achieve competitive ECP at 15 kg/m³. Increasing fiber dosage improved toughness yet intensified the trade-off between ECP and mechanical gain. The framework highlights that optimized binder composition and fiber type selection can yield carbon-efficient, structurally resilient composite systems.